Electromechanical motor

ABSTRACT

An electromechanical motor includes an actuator assembly and a body to be driven in a driving direction. The actuator assembly has an actuator backing, a first actuator and a second actuator. The actuators are mechanically attached by a respective single attachment to the actuator backing at a first end of the actuators. The actuators have a respective interaction portion constituting a second end opposite to the first end in an actuator direction transverse to the driving direction. The interaction portions are arranged for interaction with an interaction surface of the body by a respective contact area. The actuators include a respective unimorph member arranged for causing a movement of the respective contact area as a response of a respective electrical signal. The respective movements are transverse to the actuator direction, to the driving direction, and to each other.

TECHNICAL FIELD

The present invention relates to electromechanical actuator devices andmethods for driving such devices.

BACKGROUND

There are numerous applications with the need for extremely miniaturizedmotors. For example, in consumer products extremely small, low weight,low power consumption and inexpensive motors are typically requested.The motion range is often in the order of millimeters and with arequested accuracy of micrometers. A number of performance propertiesare typically requested, e.g. high speed, silent movement, low powerconsumption, easily controlled positioning and high positioningaccuracy, which to some extent are contradictory.

In order to reach highly accurate positioning that at the same time isrelatively easily controlled, different motion mechanisms are selected,such as “walking” mechanisms, stick-slip mechanisms, “inertial”positioning or stepping mechanisms. Common for most devices operatingaccording to such principles is that they involve a high degree ofstatic contacting between an actuator and a body to be moved. Theposition accuracy relies to a large extent on this static contacting.However, the speed is often relatively low, the devices often operate atsub-ultrasonic frequencies, which may make them noisy, and the powerefficiency is relatively poor. A typical example of such a device isdisclosed in the U.S. Pat. No. 6,798,117.

Such devices can with a proper driving give rise to extremely smooth andthereby quiet motion, and is perfectly suited for many high-demandapplications. Devices of this kind are generally based on a relativelycomplex motion pattern of the used actuators. This requires that severaldifferent voltage signals are provided with well defined phase shiftsand/or voltage curve shapes. Furthermore, the complex driving patternalso requests large electromechanically activatable volumes producingheat during operation. The deformation of the actuators during operationalso induce different kinds of material stress, which eventually maylead to cracking of electrodes, terminations and/or theelectromechanically active material itself.

In some applications, however, the smooth motion is not of an equallycrucial importance. Instead factors like improvements in speed,durability and complexity reductions are of higher interest.

SUMMARY

An object of the present invention is to provide low complexityminiaturized motors of reasonable speed, high durability while stillpresenting high-accurate positioning.

The above object is achieved by devices, systems and methods accordingto the enclosed independent patent claims. Preferred embodiments aredefined in the dependent patent claims. In general, according to a firstaspect, an electromechanical motor comprises an actuator assembly and abody, relative to which the actuator assembly is to be acting forcausing a relative displacement of the body in a driving direction. Theactuator assembly has an actuator backing, a first actuator and a secondactuator. The first actuator is mechanically attached by a singleattachment. The single attachment of the first actuator is a firstattachment to the actuator backing. The first attachment is provided ata first end of the first actuator. The first actuator has a firstinteraction portion constituting a second end of the first actuator. Thesecond end of the first actuator is opposite to the first end of thefirst actuator in an actuator direction. The second actuator is arrangedin an analogue manner with a second attachment and a second interactionportion. The actuator direction is transverse to the driving direction.The first interaction portion and the second interaction portion arearranged for interaction with an interaction surface of the body by arespective contact area. The first actuator and said second actuatorcomprise a respective unimorph member comprising an electromechanicalmaterial arranged between a respective first end and a respective secondend of the first actuator and the second actuator. Each of the unimorphmembers is arranged for causing a movement of a respective contact areaas a response of a respective electrical signal. The respectivemovements are transverse to the actuator direction, transverse to thedriving direction, as well as transverse to each other.

According to a second aspect, an electromechanical motor systemcomprises an electromechanical motor according to the first aspect and apower supply, connected to the electromechanical motor and arranged forproviding at least two non-identical electrical signals for excitationof the unimorph members.

According to a third aspect, A method for driving an electromechanicalmotor having a first interaction portion and a second interactionportion arranged for interacting with a body comprises the step ofproviding of a first electrical signal for exciting a unimorph membercomprising an electromechanical material attached to the firstinteraction portion and providing of a second electrical signal forexciting a unimorph member comprising an electromechanical materialattached to the second interaction portion. The first electrical signalis different from the second electrical signal. The first electricalsignal causes the unimorph member of the first interaction portion tomove a contact area of the first interaction portion in a first movementdirection transverse but not perpendicular to a driving direction. Thedriving direction is an intended forward travel direction of the bodyrelative to the first interaction portion and the second interactionportion. The second electrical signal causes the unimorph member of thesecond interaction portion to move a contact area of the secondinteraction portion in a second movement direction transverse thedriving direction. The second movement direction is transverse to thefirst movement direction. The first electrical signal and the secondelectrical are arranged for causing at least one of the firstinteraction portion and the second interaction portion to be in contactwith the body during driving.

One advantage with the present invention is that a stepping motion canbe achieved by much less complex actuator configurations, and at thesame time allow for high speed and long durability.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with further objects and advantages thereof, maybest be understood by making reference to the following descriptiontaken together with the accompanying drawings, in which:

FIG. 1 is a schematic side view of an embodiment of an electromechanicalmotor system according to the present invention;

FIGS. 2A-D are schematic illustrations of an embodiment of a ciliarymotion;

FIGS. 3A-D are diagrams showing embodiments of voltage signals forachieving a ciliary motion;

FIG. 4 is a schematic side view of another embodiment of anelectromechanical motor according to the present invention;

FIGS. 5, 6A and 6B are schematic perspective views of further otherembodiment of actuator assemblies according to the present invention;

FIG. 7 is a flow diagram of steps of an embodiment of a method accordingto the present invention; and

FIGS. 8 and 9 are schematic side views of further other embodiment ofelectromechanical motors according to the present invention.

DETAILED DESCRIPTION

Throughout the drawings, the same reference numbers are used for similaror corresponding elements.

The term “transverse” is used in its ordinary wide meaning of lying in across-wise direction, i.e. something that crosses something else, notnecessarily in a perpendicular fashion. In most cases the term can beassumed as a synonym of “non-parallel”.

A set of one-dimensionally moving actuators can with a free end act on abody for achieving a relative moving action. This type of drivingmechanism is sometimes referred to as a ciliary motion mechanism due tothe similarities to cilia systems in the nature. The one-dimensionalmotion is typically somewhat inclined with respect to the drivingdirection, in order to provide also a normal force against the surfaceto be driven. Ciliary motion may be utilized either in a resonant manneror as a stepping mechanism.

There are many examples of micromechanical system using ciliary motions.E.g. in the article “Fabrication and Operation of Polyimide BimorphActuators for a Ciliary Motion System” by M Ataka et, el. in Journal ofMicroelectromechanical systems, vol. 2, No. 4, December 1993, amicromotion system based on ciliary motion of bimorph thermal actuatorsis disclosed. In the article “A linear actuator based on ciliavibration” by T. Hatsuzawa in Sensors and Actuators A 105 (2003) pp.183-189, cilia fibres are excited by external vibrators. However, mostsuch systems have a limited positioning accuracy.

However, according to the present invention, the ciliary motion issuitable to be implemented by electromechanical actuators, e.g.piezoelectric actuators. By having actuators mechanically attached by asingle attachment to a backing provides for a firm base. By having theactuators freely movable except for that single attachment and theinteraction with the body to be moved creates possibilities to usedimensional changes in electromechanically active volumes of theactuators for creating the requested motion. Since the dimensionalchanges are essentially immediate and repeatable, very accurate motionpatterns can be achieved.

By furthermore utilizing electromechanical actuators comprising unimorphportions, a number of advantages can be achieved. The driving of aunimorph actuator requires only one voltage signal, which means that thecomplexity in the electronic control is very low. Also, the operation ofa unimorph generates a smaller amount of heat compared to a similarbimorph or multimorph structure. This in turn means that the speed canbe increased without risking overheating. The unimorph is also efficientto translate a small dimension change of an active volume into a largedisplacement of the end of the unimorph. At the same time, the unimorphwithstands high forces along the actuator, which allows for applyinghigh normal forces.

Some actuator systems based on a ciliary motion are only capable ofproviding motion in one direction. This is typically cause by the factthat most driving systems utilize pushing or pressing forces against thebody to be moved. Arrangements for other types of forces are typicallycomplex to achieve. In order to achieve a possibility to move an objectboth forwards and backwards, utilizing ciliary motion, at least twoactuators with transverse intended motion directions are requested.

An embodiment of an electromechanical motor 10 according to the presentinvention is illustrated in FIG. 1. The electromechanical motor 10comprises an actuator assembly 12 and a body 14. The actuator assembly12 is arranged to be acting on the body 14 for causing a relativedisplacement of the body 14 and actuator assembly 12 in a drivingdirection 4. The actuator assembly 12 has an actuator backing 16. Theactuator assembly 12 of the present embodiment comprises a firstactuator 20 and a second actuator 22. The actuator backing 16constitutes a support structure for the first actuator 20 and the secondactuator 22.

The first actuator 20 is mechanically attached by a single attachment.This single attachment of the first actuator 20 is a first attachment 24to the actuator backing 16. In other words, the first actuator 20 hasonly one mechanically permanent connection to the rest of the actuatorassembly 12. This configuration allows the first actuator 20 to befreely movable with the first attachment 24 as a reference point. Thefirst attachment 24 is provided at a first end 25 of the first actuator20.

The first actuator 20 has also a first interaction portion 30constituting a second end 31 of the first actuator 20. This second end31 of the first actuator 20 is opposite to the first end 25 of the firstactuator 20 as seen in an actuator direction 5. The first interactionportion 30 is arranged for interaction with an interaction surface 13 ofthe body 14 by a contact area 34. This means that the firm connection tothe actuator backing 16 and the contact area 34 against the body 14 aresituated at two opposite ends of the first actuator 20, leaving thefirst actuator without mechanical contacts between these opposite ends,i.e. between the first end 25 and the second end 31. The actuatordirection 5 is transverse to the driving direction 4, and the actuatordirection 5 is preferably perpendicular or substantially perpendicularto the driving direction 4.

The first actuator 20 comprise a unimorph member 36 comprising anelectromechanical material arranged between the first end 25 and thesecond end 31 of the first actuator 20, and preferably the entiredistance or substantially the entire distance between the first end 25and the second end 31. The unimorph member 36 of this embodimentcomprises an active volume 40, exhibiting a change in dimension as aresponse of electrical signals applied to electrodes 41 electrodesimbedded into the active volume 40. The unimorph member 36 of thisembodiment further comprises a passive volume 44 mechanically attachedto the active volume 40 along the actuator direction 5. An interface 45between the active volume 40 and the passive volume 44 thus extendsalong the entire unimorph member 36 in the actuator direction 5.

The active volume is typically built with electrodes in a multi-layerarrangement to reduce the driving voltage. The standard arrangement isto have electrodes with surfaces in the actuator direction 5, as isshown in FIG. 1. This gives a large stroke since the piezoelectriccoefficient, d₃₃, for the given orientation is large for piezoceramicmaterials such as PZT. It is also possible to arrange electrodes inother directions, e.g. in the driving direction 4 or the directionorthogonal to directions 4 and 5. In these cases the d₃₁ coefficientgives the strain and while this coefficient is somewhat lower than thed₃₃ coefficient, there are still advantages such as higher fracturestrength and easier fabrication.

Most actuator materials could be characterised as electromechanicalmaterials, but in the present disclosure we intend materials that changetheir shape when an electric voltage or current is applied. Typicalexamples of electromechanical materials are piezoelectric,electrostrictive and antiferroelectric materials and these materialscould be single crystalline as well as polycrystalline or amorphous. Thematerials of greatest interest today are polycrystalline multilayerferroelectric ceramic materials with large electromechanical strains,but there is an ongoing development of polymer and polymer compositematerials that might result in competitive properties. Piezoelectric andelectrostrictive materials are at the moment considered as the bestcandidates.

The unimorph member 36 is arranged for causing a movement of the contactarea 34 as a response of an electrical signal applied to the electrodes41. The active volume 40 changes typically its dimension in the actuatordirection when such an electrical signal is applied, but since theactive volume 40 is firmly connected to the passive volume 44 along thelength of the unimorph member 36, such dimension change instead resultsin a bending of the unimorph member 36. If the dimension change is acontraction, the unimorph member 36 bends to the left (as illustrated inthe FIG. 1), while if the dimension change is an expansion, the unimorphmember 36 bends to the right. The contact area 34 will move accordinglyand presents therefore a motion path along a first movement direction 6.This first movement direction 6 is transverse to the actuator direction5 as well as transverse to the driving direction 4. The first movementdirection 6 is furthermore non-perpendicular to the driving direction 4,which means that the movement of the contact area 34 has a component inthe driving direction 4.

The second actuator 22 is arranged in an analogue manner. In thisparticular embodiment, the first actuator 20 and the second actuator 22are arranged mirror symmetrically with respect to each other. The secondactuator 22 is therefore also mechanically attached by a singleattachment. This single attachment of the second actuator 20 is a secondattachment 26 to the actuator backing 16. The second attachment 26 isprovided at a first end 27 of the second actuator 22. The secondactuator 22 has also a second interaction portion 32 constituting asecond end 33 of the second actuator 22. This second end 33 of thesecond actuator 20 is opposite to the first end 27 of the secondactuator 22 as seen in the actuator direction 5. The second interactionportion 32 is arranged for interaction with the interaction surface 13of the body 14 by a contact area 35.

The second actuator 20 also comprise a unimorph member 38 comprising anelectromechanical material arranged between the first end 27 and thesecond end 33 of the second actuator 22. The unimorph member 38 of thisembodiment comprises an active volume 42, exhibiting a change indimension as a response of electrical signals applied to electrodes 43electrodes imbedded into the active volume 42. The unimorph member 38 ofthis embodiment further comprises a passive volume 46 mechanicallyattached to the active volume 42 along the actuator direction 5. Aninterface 47 between the active volume 42 and the passive volume 46 thusextends along the entire unimorph member 38 in the actuator direction 5.

The unimorph member 38 is arranged for causing a movement of the contactarea 35 as a response of an electrical signal applied to the electrodes43. If a dimension change of the active volume 42 as a response to theapplied electrical signal is a contraction, the unimorph member 38 bendsto the right (as illustrated in the FIG. 1), while if the dimensionchange is an expansion, the unimorph member 38 bends to the left. Thecontact area 35 will move accordingly and presents therefore a motionpath along a second movement direction 7. This second movement direction7 is transverse to the actuator direction 5 as well as transverse to thedriving direction 4. The second movement direction 7 is furthermorenon-perpendicular to the driving direction 4, which means that themovement of the contact area 35 has a component in the driving direction4.

In this particular embodiment the active volume 40 of the first actuator20 is positioned before the passive volume 44 in the driving direction4, and the active volume 42 of the second actuator 22 is positionedafter the passive volume 46 in the driving direction 4. In this manner,the first movement direction 6 is different from the second movementdirection 7. In other words, the first movement direction 6 and thesecond movement direction 7 are transverse to each other. In the presentembodiment, with the mirror symmetry, the second movement direction 7becomes a mirror direction of the first movement direction 6 withrespect to a mirror plane parallel to the actuator direction 5. In otherembodiments, the relative positions of the active and passive volumescan be the opposite, as described further below.

The active volumes 40, 42 are, as described above, activated byproviding electrical signals. To this end, an electromechanical motorsystem 1 comprising the electromechanical motor 10 also comprises apower supply 99, connected to the electromechanical motor 10 andarranged for providing at least two non-identical electrical signals forexcitation of the unimorph members 36, 38.

These one-dimensional movements of the contact areas of the actuatorscan easily be combined with relatively simple electrical signals into anarrangement operating according to a ciliary motion principle, or moreprecisely a double ciliary motion principle. FIGS. 2A-D schematicallyillustrates one embodiment of such a drive mechanism. Note that thedimension changes of the unimorphs are extremely exaggerated in thefigure, and thereby also the bending strokes, in order to clearlyillustrate the basic principles. In practice, the dimension changes andbending strokes are very small compared to the total actuatordimensions.

In FIG. 2A, both active volumes are given electrical signals causing anexpansion in the actuator direction. This causes both actuators 20, 22to bend outwards from each other. The body 14 is in contact with bothactuators 20, 22. From this position, the first actuator 20 is caused tobend back. The entire length of the first actuator 20 is also reduced,i.e. the contact area moves in the direction indicated by the arrow 100.This releases the tip of the first actuator 20 from the body 14, but thebody 14 itself does not move, since it is supported by the secondactuator 22. When the contraction of the active volume of the firstactuator 20 is ended, the first actuator is instead bent to the left,and with a shorter length, as illustrated in FIG. 2B. From thissituation, also the second actuator 22 is allowed to bend back and thecontacting area of the second actuator 22 moves along the arrow 101.Since the body 14 only is supported by the second actuator 22, the body14 follows in this motion and is thereby provided with a motioncomponent in the driving direction, as illustrated by arrow 102. We hereassume that there is a normal force holding the body 14 and the actuatorassembly 12 together.

When the bending of the second actuator 22 is ended, the situation asillustrated in FIG. 2C is achieved. The body 14 is again in contact withboth actuators 20, 22. The first actuator 20 is now given electricalsignals causing the unimorph of the first actuator to once more bend inthe direction indicated by the arrow 103. This motion also removes thecontact between the second actuator 22 and the body 14. The body therebyfollows the first actuator 20 in its motion and is thereby given amotion component 104 in the driving direction. The situation of FIG. 2Dis eventually reached. Here the second actuator 22 is caused to bendagain for retrieving its original position from FIG. 2A, by the motion105. The situation of FIG. 2A is again achieved, however, now with thebody moved a certain distance in the driving direction.

In such a way, a driving action can be achieved. By reversing theapplication of the electrical signals, the driving action can also beprovided in the opposite direction.

In FIG. 3A, two voltage curves are illustrated as an embodiment of howthe driving voltages of the first and second actuator may look like. Theupper one refers to the voltage applied over the first actuator of FIGS.2A-D and the lower one refers to the voltage applied over the secondactuator. A positive voltage is here assumed to cause an expansion ofthe active volume, and a negative voltage is assumed to cause acontraction of the active volume. The letters below the time axis refersto the different situation of FIGS. 2A-D. A single voltage curve, phaseshifted 90 degrees between the two actuators can thus be used forcausing a stepping action. A minor disadvantage with such an embodimentis that the body is only actively driven during half the period (betweenB and D), while is it standing still the rest of the time (between A andB and between D and A).

FIG. 3B illustrates another embodiment of driving voltages. Here thetimes between the situations A-D are modified so that the periods whenthe body is at rest are reduced and optionally the active moving periodscan be increased. A faster or at least smoother movement of the body isachieved. In such a case, however, it is no longer possible to use anidentical shape of the voltages to the different actuator. Insteadseparate curve shapes have to be provided.

FIG. 3C illustrates yet another embodiment of driving voltages. Thesevoltages cause a double ciliary motion with the actuators describedbefore, however, in a slightly different manner as what is illustratedin FIGS. 2A-D. The situations of FIGS. 2B and 2D will actually not bereached. In this embodiment, the operation of contracting the secondactuator starts just a short while, at time E, after the contraction ofthe first actuator starts. When the first actuator reaches its mostcontracted state at time F, the second actuator is also almost fullycontracted. The body will nevertheless be in contact with only thesecond actuator until the situation of FIG. 2C is reached. The firstactuator starts to expand and takes over the contact to the body. Attime G, also the second actuator starts to expand and when the firstactuator reaches its most expanded state at time H, the second actuatoris also almost fully expanded. The period during which the body is atrest is limited to the time between H and E of the following cycle.

FIG. 3D illustrates another embodiment of a similar theme. Here thevoltages are optimized to give a minimum resting time. The personskilled in the art realizes that there are numerous variations of how toapply the voltages to achieve a double ciliary motion. Even phaseshifted simple wave forms, such as sinusoidal or triangular voltagecurves can be used. In some such cases, the motion of the body may besomewhat strange, with parts of reciprocal motion periods, but maynevertheless be used to achieve a net motion in a pre-determineddirection.

Here above, the described motion patterns are achieved using unimorphs,i.e. members having an electromechanically passive part integrated inone and the same piece as an electromechanically active part. The samekind of motion pattern would also be possible to achieve by moreelaborate actuators, such as e.g. bimorphs, having two mechanicallyconnected active parts. However, such arrangements are more complex todrive and do not provide all the stability advantages as the unimorphsdo, see the description further below. Therefore, unimorphs are thepresently preferred building block for the ideas of the presentinvention.

The use of unimorphs has certain advantages, in particular if theactuator direction is perpendicular or essentially perpendicular to thedriving direction. The passive parts of the actuator provide a rigidsupport for even relatively high normal forces between the actuatorassembly and the body. At the same time, the very same members are themembers causing the movement that is parallel to neither the actuatordirection nor the driving direction. Further advantages of furtherpreferred embodiments are presented here below.

In the embodiment of FIG. 1, the active volumes of the actuators arefacing each other, which means that the first and second movementdirections 6, 7 associated with an expansion of the active volumes aredirected from each other. The opposite is of course also possible, asillustrated by FIG. 4. Here the active volumes 40, 42 of the actuators20, 22 are facing away from each other. This results in that the firstand second movement directions 6, 7 also are directed in mirrorsymmetrical directions compared with what is the situation in FIG. 1.

In FIG. 4, the contact areas 34, 35 of the interaction portions 30, 32are provided close to the outer edge of the respective actuator 20, 22.In other words, the contact areas are situated offset in a directionalong the driving direction 4 from a centre line 3 of respectiveactuator to 20, 22, to which it is attached. This arrangement has theadvantage that an increased levering action is achieved. The positionsat which the contact areas 34, 35 are positioned present a larger strokethan a contact area positioned at the centre line 3. In such a manner,the step size of each cycle can be increased, which also increases themaximum achievable speed.

This property is further developed in FIG. 5, where the interactionportions 30, 32 are allowed to extend outside the main actuatorcross-section. The first interaction portion 30 has a protruding portion37, protruding outside the first actuator 20 in a direction along thedriving direction 4, in this case opposite to the indicated drivingdirection 4. The contact area 34 of the first interaction portion 30 isprovided at that protruding portion 37. Similarly, the secondinteraction portion 32 has a protruding portion 39, protruding outsidethe second actuator 22 in a direction along the driving direction 4, inthis case opposite to the indicated driving direction 4. The contactarea 35 of the second interaction portion 30 is provided at thatprotruding portion 39. In such an embodiment, the levering action isfurther increased. However, at the same time, the ability to withstandnormal forces will be reduced, since the normal force will act outsidethe cross-section of the main actuator, which means that the normalforce will give rise to a bending torque.

In FIG. 5, it can also be seen that the width of the actuator in thedirection of the driving direction 4 is kept relatively small, while thewidth in a cross direction 2 perpendicular to both the driving direction4 and the actuator direction 5 is relatively large. Such a shapeincrease the possible bending of the actuators, which together with theprotruding portions 37, 39 give rise to very large possible steps.

Another feature that preferably can be utilized for further increasingthe efficiency is the design of the electrodes 41, 43. In manyapplications using multilayer techniques for achieving e.g. bimorphstructures, the electrodes are “hidden” within the active volume inorder to connect one of the electrodes, either the phase or groundelectrode, with the termination electrode 29 without causingshort-circuits. This is usually called an interdigital electrodearrangement. The problem with this is that the dimension changes in thisouter in-active layer causes large tensile stresses that increase therisks for cracks at the actuator surfaces. These cracks are typicallyappearing at positions where terminations are provided, which may causefailure of the actuators or terminations.

At the contrary, in the present disclosure, in embodiments when passivevolumes 44, 46 are available in the actuators 20, 22, the surfaces ofthe passive volumes 44, 46 can be utilized for providing terminations29, by which the electrodes 41, 43 are electrically connected. Here therisk for cracks is lower, in particular in the vicinity of the middle ofthe passive volume 44, 46. By providing the terminations 29 at thepassive volumes 44, 46, the electrodes 41, 43 can in many applicationsbe allowed to extend all the way out to at least one outer surface ofthe active volume, and preferably to all outer surfaces. In particular,the electrodes can extend 41, 43 out to at least one of a surface 51 ofthe active volume 40, 42 facing away from the corresponding passivevolume 44, 46, and a surface 50 of the active volume 40, 42 along thedriving direction 4. The provision of the electrodes the entire way outto the surface of the active volume 40, 42 has two main advantages.First, a larger volume of the electromechanically active material can beutilized for causing a motion. Secondly, any inactive layer of materialoutside the electrodes will counteract any shape changes of the activevolume, and the reduction of such zones also makes the motion moreefficient.

In a typical application, the body is at least partially supported bysome bearing arrangement. It is then of great importance to have thecontact areas well aligned with the interaction surface 13 at theinstants when both contact areas 34, 35 are in contact with the body 14.This occurs typically at minimum and maximum strokes. If the alignmentis poor, there is a risk that only one of the contact areas 34, 35 is incontact with the body, and the transfer of contact between the twocontact areas 34, 35 will not take place according to the intendedschedule. A very accurate alignment of the interaction surface 13 of thebody 14 might therefore be necessary in a general case.

In an embodiment, illustrated in FIG. 6A, such alignment requirementsare no longer so strict. In this embodiment, both the first actuator 20and the second actuator 22 are provided with respective interactionportions 30, 32 having protruding portions 37, 39. The contact area 34of the interaction portion 30 of the first actuator 20 is here alignedwith the contact area 35 of the interaction portion 32 of the secondactuator 22 in the cross direction 2. If the interaction surface 13 ofthe body is somewhat inclined from the intended perpendicularconfiguration, the same height differences will be experienced by bothinteraction surfaces. This in turn means that any handing-overprocedures between the contact areas 34, 35 will proceed just as plannedwithout disturbances.

FIG. 6B illustrates another embodiment presenting a similar alignmentrobust configuration of the contact areas 34, 35. Here, the contact area34 of the first interaction portion 30 and the contact area 35 of saidsecond interaction portion 32 comprise respective part contact areas,being interleaved with each other in the cross direction 2.

FIG. 7 illustrates a flow diagram of steps of an embodiment of a methodaccording to the present invention. The method for driving anelectromechanical motor having a first interaction portion and a secondinteraction portion arranged for interacting with a body is started instep 200. In step 210, a first electrical signal for exciting a unimorphmember attached to said first interaction portion is provided. In step212, a second electrical signal for exciting a unimorph member attachedto said second interaction portion is provided. The steps 210 and 212are performed simultaneously and in typically in cooperation. The firstelectrical signal is different from the second electrical signal. Thefirst electrical signal causes in step 214 the unimorph member of thefirst interaction portion to move a contact area of the firstinteraction portion in a first movement direction transverse but notperpendicular to a driving direction. The driving direction is anintended forward travel direction of the body relative to the firstinteraction portion and the second interaction portion. Similarly thesecond electrical signal causes in step 216 the unimorph member of thesecond interaction portion to move a contact area of the secondinteraction portion in a second movement direction transverse thedriving direction. The second movement direction is transverse also tothe first movement direction. The first electrical signal and the secondelectrical are arranged for causing, in step 218, at least one of thefirst interaction portion and the second interaction portion to be incontact with the body during driving. The procedure ends in step 299.

There are many different possible variations of the double ciliarymotion motor presented in the present disclosure. It is e.g. not limitedto have just two actuators. Also multiple-actuator solutions arepossible. FIG. 8 illustrates one embodiment of an electromechanicalmotor having four actuators. In this embodiment, the actuators areelectrically connected in two pairs, thereby providing a correspondingmotion scheme as described above. The cooperating actuators can beplaced in any configuration with respect to each other, preferablyselected dependent on the intended application. In the presentembodiment, all four actuators are placed in a line. However,configurations of actuators provided at different two-dimensionalpositions are also possible. When the different groups of actuator pairsare operating out of phase with each other a smoother movement can beachieved.

In the above embodiments, the actuators are illustrated in aperpendicular relation to the interaction surface of the body. Asmentioned above, this gives advantages in terms of loads. However, inother applications, e.g. where the load is very small, other geometricalconfigurations are also possible. An embodiment of FIG. 9 illustrates anelectromechanical motor having two non-parallel actuators, whichfurthermore are non-perpendicular to the interaction surface 13. In thismanner it is possible to use also geometrical design for determine theinclining angle between the movement directions 6, 7 of the contactareas 34, 35 and the driving direction 4.

By having access to more than one pair of actuators, it is also possibleto achieve motion in more than one direction. One pair of actuators canthen be used for moving the object in a first driving direction, whileanother pair of actuators can be used for moving the object in atransversal driving direction. The unimorphs are then aligned in theintended driving direction.

Another possibility to achieve a two-dimensional motion is to providethe actuators with a bimorph structure in the cross section. Such anembodiment is illustrated in FIG. 10. The active volume of each actuatoris divided in two part active volumes in the cross direction 2. The partactive volumes are arranged to be excited by separate electricalsignals. If the signals are different, this will result in a bending ofthe actuators in the cross direction 2. By adapting the electricalsignals, a motion in a direction transverse to the driving direction canthus be allowed.

The embodiments described above are to be understood as a fewillustrative examples of the present invention. It will be understood bythose skilled in the art that various modifications, combinations andchanges may be made to the embodiments without departing from the scopeof the present invention. In particular, different part solutions in thedifferent embodiments can be combined in other configurations, wheretechnically possible. The scope of the present invention is, however,defined by the appended claims.

The invention claimed is:
 1. An electromechanical motor, comprising: anactuator assembly; a body, relative to which said actuator assembly isto be acting for causing a relative displacement of said body in adriving direction; said actuator assembly having an actuator backing, afirst actuator and a second actuator; said first actuator ismechanically attached by a single attachment; said single attachment ofsaid first actuator is a first attachment to said actuator backing, saidfirst attachment being provided at a first end of said first actuator;said first actuator having a first interaction portion constituting asecond end of said first actuator, said second end of said firstactuator being opposite to said first end of said first actuator in anactuator direction; said second actuator is mechanically attached by asingle attachment; said single attachment of said second actuator is asecond attachment to said actuator backing, said second attachment beingprovided at a first end of said second actuator; said second actuatorhaving a second interaction portion constituting a second end of saidsecond actuator, said second end of said second actuator being oppositeto said first end of said second actuator in said actuator direction;said actuator direction being transverse to said driving direction; saidfirst interaction portion and said second interaction portion beingarranged for interaction with an interaction surface of said body by arespective contact area; said first actuator and said second actuatorcomprise a respective member comprising an electromechanical materialarranged between a respective said first end and a respective saidsecond end of said first actuator and said second actuator; each of saidmembers that comprises an electromechanical material being arranged forcausing a one-dimensional movement forth and back of a respective saidcontact area as a response of a respective single electrical signal; andsaid respective one-dimensional movements are transverse to saidactuator direction, transverse to said driving direction, as well astransverse to each other; each of said members that comprises anelectromechanical material comprises an active volume, exhibiting achange in dimension as a response of said single electrical signalapplied thereto, and a passive volume mechanically attached to arespective said active volume along said actuator direction; said activevolume of said first actuator is positioned before said passive volumein said driving direction; and said active volume of said secondactuator is positioned after said passive volume in said drivingdirection.
 2. The electromechanical motor according to claim 1, wherein:at least one of said active volume of said first actuator and saidactive volume of said second actuator comprises electrodes for excitingsaid active volume imbedded into said active volume; said electrodesextending out to at least one of: a surface of said active volume facingaway from said passive volume attached to the active volume; and asurface of said active volume along said driving direction.
 3. Theelectromechanical motor according to claim 2, wherein said electrodesare electrically connected to terminations provided at a surface of saidpassive volume.
 4. The electromechanical motor according to claim 1,wherein at least one contact area of said first interaction portion andsaid second interaction portion is situated offset in a direction alongsaid driving direction from a center line of respective said actuator towhich it is attached.
 5. The electromechanical motor according to claim4, wherein at least one of said first interaction portion and saidsecond interaction portion has a protruding portion, protruding outsidethe respective actuator to which it is attached in a direction alongsaid driving direction.
 6. The electromechanical motor according toclaim 5, wherein said contact area of said at least one of said firstinteraction portion and said second interaction portion is provided atsaid protruding portion.
 7. The electromechanical motor according toclaim 5, wherein both said first interaction portion and said secondinteraction portion has a respective said protruding portion.
 8. Theelectromechanical motor according to claim 7, wherein said contact areaof said first interaction portion is aligned with said contact area ofsaid second interaction portion in a cross direction, perpendicular tosaid driving direction.
 9. The electromechanical motor according toclaim 8, wherein said contact area of said first interaction portion andsaid contact area of said second interaction portion comprise respectivepart contact areas, being interleaved with each other.
 10. Anelectromechanical motor system comprising: an electromechanical motorhaving an actuator assembly, a body, relative to which said actuatorassembly is to be acting for causing a relative displacement of saidbody in a driving direction, said actuator assembly having an actuatorbacking, a first actuator and a second actuator, said first actuator ismechanically attached by a single attachment, said single attachment ofsaid first actuator is a first attachment to said actuator backing, saidfirst attachment being provided at a first end of said first actuator,said first actuator having a first interaction portion constituting asecond end of said first actuator, said second end of said firstactuator being opposite to said first end of said first actuator in anactuator direction, said second actuator is mechanically attached by asingle attachment, said single attachment of said second actuator is asecond attachment to said actuator backing, said second attachment beingprovided at a first end of said second actuator, said second actuatorhaving a second interaction portion constituting a second end of saidsecond actuator, said second end of said second actuator being oppositeto said first end of said second actuator in said actuator direction,said actuator direction being transverse to said driving direction, saidfirst interaction portion and said second interaction portion beingarranged for interaction with an interaction surface of said body by arespective contact area, said first actuator and said second actuatorcomprise a respective member comprising an electromechanical materialarranged between a respective said first end and a respective saidsecond end of said first actuator and said second actuator, each of saidmembers that comprises an electromechanical material being arranged forcausing a one-dimensional movement forth and back of a respective saidcontact area as a response of a respective single electrical signal,said respective one-dimensional movements are transverse to saidactuator direction, transverse to said driving direction, as well astransverse to each other, each of said members that comprises anelectromechanical material comprises an active volume, exhibiting achange in dimension as a response of said single electrical signalapplied thereto, and a passive volume mechanically attached to arespective said active volume along said actuator direction, said activevolume of said first actuator is positioned before said passive volumein said driving direction, and said active volume of said secondactuator is positioned after said passive volume in said drivingdirection; and a power supply, connected to said electromechanical motorand arranged to provide at least two non-identical electrical signalsfor excitation of said members that comprise an electromechanicalmaterial.
 11. A method for driving an electromechanical motor having afirst interaction portion and a second interaction portion arranged forinteracting with a body, said method comprising the steps of: providinga first electrical signal for exciting a member comprising anelectromechanical material attached to said first interaction portion;and providing a second electrical signal for exciting a membercomprising an electromechanical material attached to said secondinteraction portion; said first electrical signal is different from saidsecond electrical signal; each of said members that comprises anelectromechanical material comprises an active volume that exhibits achange in dimension as a response to said first and second electricalsignals respectively applied thereto, and a passive volume mechanicallyattached to a respective said active volume along an actuator direction;said first electrical signal and said second electrical being arrangedfor causing at least one of said first interaction portion and saidsecond interaction portion to be in contact with said body duringdriving; said first electrical signal causes said member that comprisesan electromechanical material of said first interaction portion to movea contact area of said first interaction portion forth and back in afirst one-dimensional movement direction transverse but notperpendicular to a driving direction, said driving direction being anintended forward travel direction of said body relative to said firstinteraction portion and said second interaction portion; and said secondelectrical signal causes said member that comprises an electromechanicalmaterial of said second interaction portion to move a contact area ofsaid second interaction portion forth and back in a secondone-dimensional movement direction transverse to said driving direction,said second one-dimensional movement direction being transverse to saidfirst one-dimensional movement direction.